Hong Kong's district court found that one officer had stamped on 40-year-old Tsang and that four other officers kicked him. Two other officers did not participate but watched.

"Every police officer has a duty to prevent the commission of a crime, even by fellow police officers," a press summary of the verdict said.

Judge David Dufton said in court that Tsang suffered injuries to his face, neck and body during the assault.

"The court was not however satisfied these injuries amounted to grievous bodily harm but was satisfied they amounted to actual bodily harm," he said.

The charge carries a maximum sentence of three years.

One of the officers who kicked Tsang was also found guilty of common assault for slapping him in the face twice after he was taken to a police station.

Tsang, a social worker, was himself was found guilty last year of assaulting and resisting officers on the same night, when he splashed liquid on police. He was given a five-week sentence and has said he will appeal.

Tsang was not in court for Tuesday's verdict. He has always argued that police brought assault charges against him to distract from the case against them.

Rival protesters gathered outside the court, with pro-police supporters outnumbering a small group of democracy demonstrators.

Using loudspeakers they chanted: "Support the seven officers" and "Reasonable enforcement of the law".

Nearly 1,000 people were arrested over the course of the 2014 protests.

Rally leaders Nathan Law, Joshua Wong and Alex Chow were all convicted in August for taking part in, or inciting others to take part in, a protest that led up to the major demonstrations.

They were given community service or suspended sentences after the magistrate said she believed they had been "genuinely expressing their views" during the protest, which saw students climb over a fence into the Hong Kong government complex.